LE Magazine June 2002
Six-month oral dehydroepiandrosterone supplementation in early and late postmenopause.
The adrenal production of the delta 5-androgens, dehydroepiandrosterone (DHEA) and its sulfate ester dehydroepiandrosterone sulfate (DHEAS), declines linearly with aging. The evidence that DHEA or DHEAS administration may alleviate some of the problems related to aging has opened new perspectives for clinical research. The present study aims to investigate the effects of a 6-month DHEA supplementation in early and late postmenopausal women, with normal or overweight body mass index (BMI), on the level of circulating steroids, sex hormone binding globulin (SHBG), beta-endorphin and gonadotropins, and on the adrenal gland response to dexamethasone suppression and adrenocorticotropic hormone (ACTH) stimulation. Early postmenopausal women (50-55 years) both normal weight (BMI 20-24, n = 9) and overweight (BMI 26-30, n = 9) and late postmenopausal women (60-65 years) both of normal weight and overweight, were treated with oral DHEA (50 mg/day). Circulating DHEA, DHEAS, 17-OH pregnenolone, progesterone, 17-OH progesterone, allopregnenolone, androstenedione, testosterone, dihydrotestosterone, estrone, estradiol, SHBG, cortisol, luteinizing hormone, follicle stimulating hormone and beta-endorphin levels were evaluated monthly and a Kupperman score was performed. The product/precursor ratios of adrenal steroid levels were used to assess the relative activities of the adrenal cortex enzymes. Before and after 3 and 6 months of therapy, each women underwent an ACTH stimulating test (10 micrograms i.v. in bolus) after dexamethasone administration (0.5 mg p.o.) to evaluate the response of cortisol, DHEA, DHEAS, androstenedione, 17-OH pregnenolone, allopregnanolone, progesterone and 17-OH progesterone. The between-group differences observed before treatment disappeared during DHEA administration. Levels of 17-OH pregnenolone remained constant during the 6 months. Levels of DHEA, DHEAS, androstenedione, testosterone and dihydrotestosterone increased progressively from the first month of treatment. Levels of estradiol and estrone significantly increased after the first/second month of treatment. Levels of SHBG significantly decreased from the second month of treatment only in overweight late postmenopausal women, while the other groups showed constant levels. Progesterone levels remained constant in all groups, while 17-OH progesterone levels showed a slight but significant increase in all groups. Allopregnanolone and plasma beta-endorphin levels increased progressively and significantly in the four groups, reaching values three times higher than baseline. Levels of cortisol and gonadotropins progressively decreased in all groups. The product/precursor ratios of adrenal steroid levels at the sixth month were used to assess the relative activities of the adrenal cortex enzymes and were compared to those found before therapy. The 17,20-desmolase, sulfatase and/or sulfotransferase, 17,20-lyase and 5 alpha-reductase activities significantly increased, while the 3 beta-hydroxysteroid-oxidoreductase activity did not vary. On the contrary, the 11-hydroxylase and/or 21-hydroxylase activities showed a significant decrease after 6 months of treatment. In basal conditions, dexamethasone significantly suppressed all the adrenal steroids and this suppression was greater after 3 and 6 months of treatment for DHEA, DHEAS and allopregnanolone, while it remained unchanged for other steroids. Before treatment, ACTH stimulus induced a significant response in all parameters; after the treatment, it prompted a greater response in delta 5- and delta 4-androgens, progesterone and 17-OH progesterone, while cortisol responded less in both younger and older normal-weight women. The endometrial thickness did not show significant modifications in any of the groups of postmenopausal women during the 6 months of treatment. Treatment with DHEA was associated with a progressive improvement of the Kupperman score in all groups, with major effects on the vasomotor symptoms in.
Gynecol Endocrinol 2000 Oct;14(5):342-63
Cell nonautonomy of C. elegans daf-2 function in the regulation of diapause and life span.
The insulin/IGF receptor homolog DAF-2 regulates the aging in C. elegans. Decreasing daf-2 activity causes fertile adults to remain active much longer than normal and to live more than twice as long. A more severe decrease in daf-2 function causes young larvae to enter a state of diapause rather than progressing to adulthood. We have asked which cells require daf-2 gene activity in order for the animal to develop to adulthood and to age normally. We found that daf-2 functions nonautonomously in both processes. Our findings imply that the life span of C. elegans is determined by a signaling cascade in which the DAF-2 receptor acts in multiple cell lineages to regulate the production or activity of a secondary signal (or signals), which, in turn, controls the growth and longevity of individual tissues in the animal.
Cell 1998 Oct 16;95(2):199-210
Regulation of life span by sensory perception in Caenorhabditis elegans.
Caenorhabditis elegans senses environmental signals through ciliated sensory neurons located primarily in sensory organs in the head and tail. Cilia function as sensory receptors, and mutants with defective sensory cilia have impaired sensory perception. Cilia are membrane-bound microtubule-based structures and in C. elegans are only found at the dendritic endings of sensory neurons. Here we show that mutations that cause defects in sensory cilia or their support cells, or in sensory signal transduction, extend life span. Our findings imply that sensory perception regulates the life span of this animal, and suggest that in nature, its life span may be regulated by environmental cues.
Nature 1999 Dec 16;402(6763):804-9
REF-1, a protein with two bHLH domains, alters the pattern of cell fusion in C. elegans by regulating Hox protein activity.
Hox genes control the choice of cell fates along the anteroposterior (AP) body axis of many organisms. In C. elegans, two Hox genes, lin-39 and mab-5, control the cell fusion decision of the 12 ventrally located Pn.p cells. Specific Pn.p cells fuse with an epidermal syncytium, hyp7, in a sexually dimorphic pattern. In hermaphrodites, Pn.p cells in the mid-body region remain unfused whereas in males, Pn.p cells adopt an alternating pattern of syncytial and unfused fates. The complexity of these fusion patterns arises because the activities of these two Hox proteins are regulated in a sex-specific manner. MAB-5 activity is inhibited in hermaphrodite Pn.p cells and thus MAB-5 normally only affects the male Pn.p fusion pattern. Here we identify a gene, ref-1, that regulates the hermaphrodite Pn.p cell fusion pattern largely by regulating MAB-5 activity in these cells. Mutation of ref-1 also affects the fate of other epidermal cells in distinct AP body regions. ref-1 encodes a protein with two basic helix-loop-helix domains distantly related to those of the hairy/Enhancer of split family. ref-1, and another hairy homolog, lin-22, regulate similar cell fate decisions in different body regions along the C. elegans AP body axis.
Development 2001 May;128(10):1793-804
The age-1 and daf-2 genes function in a common pathway to control the life span of Caenorhabditis elegans.
Recessive mutations in two genes, daf-2 and age-1, extend the life span of Caenorhabditis elegans significantly. The daf-2 gene also regulates formation of an alternative developmental state called the dauer. Here we asked whether these two genes function in the same or different life span pathways. We found that the longevity of both age-1 and daf-2 mutants requires the activities of the same two genes, daf-16 and daf-18. In addition, the daf-2(e1370); age-1(hx546) double mutant did not live significantly longer than the daf-2 single mutant. We also found that, like daf-2 mutations, the age-1(hx546) mutation affects certain aspects of dauer formation. These findings suggest that age-1 and daf-2 mutations do act in the same life span pathway and extend life span by triggering similar if not identical processes.
Genetics 1995 Dec;141(4):1399-406
Genetic pathways that regulate aging in model organisms.
Searches for genes involved in the aging process have been made in genetically tractable model organisms such as yeast, the nematode Caenorhabditis elegans, Drosophila melanogaster fruitflies and mice. These genetic studies have established that ageing is indeed regulated by specific genes, and have allowed an analysis of the pathways involved, linking physiology, signal transduction and gene regulation. Intriguing similarities in the phenotypes of many of these mutants indicate that the mutations may also perturb regulatory systems that control ageing in higher organisms.
Nature 2000 Nov 9;408(6809):255-62
Signals from the reproductive system regulate the life span of C. elegans.
Understanding how the ageing process is regulated is a fascinating and fundamental problem in biology. Here we demonstrate that signals from the reproductive system influence the life span of the nematode Caenorhabditis elegans. If the cells that give rise to the germ line are killed with a laser microbeam, the life span of the animal is extended. Our findings suggest that germline signals act by modulating the activity of an insulin/IGF-1 (insulin-like growth factor) pathway that is known to regulate the aging of this organism. Mutants with reduced activity of the insulin/IGF-1-receptor homologue DAF-2 have been shown to live twice as long as normal, and their longevity requires the activity of DAF- 16, a member of the forkhead/winged-helix family of transcriptional regulators. We find that, in order for germline ablation to extend life span, DAF-16 is required, as well as a putative nuclear hormone receptor, DAF-12. In addition, our findings suggest that signals from the somatic gonad also influence aging, and that this effect requires DAF-2 activity. Together, our findings imply that the C. elegans insulin/IGF-1 system integrates multiple signals to define the animal’s rate of aging. This study demonstrates an inherent relationship between the reproductive state of this animal and its life span, and may have implications for the
co-evolution of reproductive capability and longevity.
Nature 1999 May 27;399(6734):362-6
A C. elegans mutant that lives twice as long as wild type.
We have found that mutations in the gene daf-2 can cause fertile, active, adult Caenorhabditis elegans hermaphrodites to live more than twice as long as wild type. This life span extension, the largest yet reported in any organism, requires the activity of a second gene, daf-16. Both genes also regulate formation of the dauer larva, a developmentally arrested larval form that is induced by crowding and starvation and is very long-lived. Our findings raise the possibility that the longevity of the dauer is not simply a consequence of its arrested growth, but instead results from a regulated life span extension mechanism that can be uncoupled from other aspects of dauer formation. daf-2 and daf-16 provide entry points into understanding how life span can be extended.
Nature 1993 Dec 2;366(6454):461-4
Regulation of the Caenorhabditis elegans longevity protein DAF-16 by insulin/IGF-1 and germline signaling.
The life span of Caenorhabditis elegans is regulated by the insulin/insulin-like growth factor (IGF)-1 receptor homolog DAF-2, which signals through a conserved phosphatidylinositol 3-kinase (PI 3-kinase)/Akt pathway. Mutants in this pathway remain youthful and active much longer than normal animals and can live more than twice as long. This life span extension requires DAF-16, a forkhead/winged-helix transcription factor. DAF-16 is thought to be the main target of the DAF-2 pathway. Insulin/IGF-1 signaling is thought to lead to phosphorylation of DAF-16 by AKT activity, which in turn shortens life span. Here, we show that the DAF-2 pathway prevents DAF-16 accumulation in nuclei. Disrupting Akt-consensus phosphorylation sites in DAF-16 causes nuclear accumulation in wild-type animals, but, surprisingly, has little effect on life span. Thus the DAF-2 pathway must have additional outputs. Life span in C. elegans can be extended by perturbing sensory neurons or germ cells. In both cases, life span extension requires DAF-16. We find that both sensory neurons and germline activity regulate DAF-16 accumulation in nuclei, but the nuclear localization patterns are different. Together these findings reveal unexpected complexity in the DAF-16-dependent pathways that regulate aging.
Nat Genet 2001 Jun;28(2):139-45
Regulation of C. elegans life span by insulin-like signaling in the nervous system.
An insulin-like signaling pathway controls Caenorhabditis elegans aging, metabolism, and development. Mutations in the daf-2 insulin receptor-like gene or the downstream age-1 phosphoinositide 3-kinase gene extend adult life span by two- to three-fold. To identify tissues where this pathway regulates aging and metabolism, we restored daf-2 pathway signaling to only neurons, muscle, or intestine. Insulin-like signaling in neurons alone was sufficient to specify wild-type life span, but muscle or intestinal signaling was not. However, restoring daf-2 pathway signaling to muscle rescued metabolic defects, thus decoupling regulation of life span and metabolism. These findings point to the nervous system as a central regulator of animal longevity.
Science 2000 Oct 6;290(5489):147-50
Patterning C. elegans: homeotic cluster genes, cell fates and cell migrations.
Despite its simple body form, the nematode C. elegans expresses homeotic cluster genes similar to those of insects and vertebrates in the patterning of many cell types and tissues along the anteroposterior axis. In the ventral nerve cord, these genes program spatial patterns of cell death, fusion, division and neurotransmitter production; in migrating cells they regulate the direction and extent of movement. Nematode development permits an analysis at the cellular level of how homeotic cluster genes interact to specify cell fates, and how cell behavior can be regulated to assemble an organism.
Trends Genet 1994 May;10(5):159-64
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